When polymers are prepared by normal slurry polymerization technique, the system consists of two phases: the diluent phase and the solid polymer particle phase. The diluent phase may consist of monomers only or monomers dissolved in a hydrocarbon medium. The diluent, therefore, is a solvent for the monomers and catalysts but a nonsolvent for the polymer formed.
In slurry polymerization, the particles are generally not stabilized and tend to agglomerate to form a polymer paste or slurry that comprises a mass of sticky polymer particles that are swollen by the monomer. A common problem created by this type of product is the adherence of the polymer particles to the reactor walls and the agitation equipment in the reactor as well as the plugging of transfer lines, valves, and pumps. Needless to say, this causes severe maintenance problems. Since control of reaction temperature is of a major concern in a polymerization process, the swollen mass of polymer particles can also create additional heat transfer problems since a build-up thereof on reactor walls would lower the overall heat transfer coefficient for the reaction system.
It is, therefore, desirable to conduct two-phase slurry polymerization whereby polymer build-up on reactor walls and agitation equipment within the reactor is reduced to lessen maintenance problems and reactor clean-up. It is also desirable to conduct slurry polymerization in a manner whereby a dispersion is produced of fine polymer particles suspended in the diluent whereby, in a preferred embodiment, the dispersion is stable, i.e., where the polymer particles do not settle out immediately following the cessation of agitation. It is also desirable to produce a dispersion product prepared in the presence of a dispersant wherein the polymer particles are much smaller than in a dispersion product prepared in absence of a dispersant. The term "dispersion" polymerization will be used hereinafter to denote polymerization reactions wherein a dispersant is used to attain a dispersion of slurry polymer particles.